Methods and apparatus for producing corrugated metal tubes

ABSTRACT

THE PRESENT INVENTION RELATES TO METHODS AND APPARATUS FOR PRODUCING CORRUGATIONS IN METALLIC TUBES AND IS CHARACTERIZED BY THE FACT THAT IT IS POSSIBLE TO PRODUCE CORRUGATIONS OF VARIOUS SHAPES BY UTILIZING AT LEAST TWO CORRUGATING RINGS OR TWO SETS OF CORRUGATING ROLLS. IN PARTICULAR THE INVENTION RELATES TO METHODS AND APPARATUS CAPABLE OF PRODUCING EASILY CORRUGATIONS OF GREATER DEPTH AS COMPARED WITH PITCH, CORRUGATIONS OF A SMALL PITCH WHOSE TROUGH IS WIDER THAN THE CREST (TUBES WITH SUCH CORRUGATIONS HAVE GOOD BENDING CHARACTERISTICS AND OTHER MECHANICAL PROPERTIES AND PERMIT A CABLE TO BE PULLED INTO THEM MORE EASILY), AND FURTHERMORE CORRUGATIONS CONFORMABLE TO THE SHAPES OF APEXES OF CORRUGATING RINGS OR ROLLS, WITHOUT EMPLOYING ANY CORE (CORRUGATING TOOL TO BE APPLIED INSIDE THE TUBE) AS IN THE CONVENTIONAL APPARATUS.

March'Q, 1971 susuMu roan- 3,563,439

METHODS AND APPARATUS FOR PRODUCING CORRUGATED METAL TUBES Filed Aug. 12, 1968 7 Sheets-Sheet 1 INVENTOR 52150777214 55 Z fa ATTORNEY March 1971 susuMu TOBITA METHODS AND APPARATUS FOR PRODUCING CORRUGATED METAL TUBES Filed Aug. 12, 1968 7 Sheets-Sheet 2 FIG. 2b

INVENTOR 5215 a mu 75 z fa ATTORNEY March 9,1971 susuMu TOBITA 3,568,489

METHODS AND APPARATUS FOR PRODUCING CORRUGATED METAL TUBES Filed Aug. 12, 1968 7 Sheets-Sheet 8 INVENTOR 52/54/771 1/ 70461 {a ATTORNIz'Y March 971 SUSUMU TOBlTA 3,568,489

METHOD5 AND APPARATUS FOR PRODUCING CORRUGATED METAL TUBES Filed Aug. 12, 1968 7 Sheets-Sheet 6 INVENTOR 51152117711 6&1/(1

ATTORNEY Mar h 9, 1 71 susuMu TOBITA,

METHODS AND APPARATUS FOR PRODUCING CORRUGATED METAL TUBES Filed Aug. 12, 1968 7 Sheets-Sheet 5 INVENTOR 54/50/72 u 76$! fa,

ATTORNEY March 9, 1971 susuMu TOBITA METHODS AND APPARATUS FOR PRODUCING CORRUGATED METAL TUBES 7 Sheets- Sheet 6 Filed Aug. 12, 1968 INVENTOR J N. 1/ /(J/)z fa ATTOR N I Y March 9, 1971 susuMu TOBlTA 3,568,489

METHODS AND APPARATUS FOR PRODUCING CORRUGATED METAL TUBES Filed Aug. 12, 1968 7 Sheets-Sheet '7 INVENTOR fusuzrzu 75.51 [a mfw ATTORNEY United States Patent Ofice 3,568,489 METHODS AND APPARATUS FOR PRODUCING CORRUGATED METAL TUBES Susumu Tobita, 136 Mitsusawa, Nishi-machi, Japan Filed Aug. 12, 1968, Ser. No. 752,044 Claims priority, application Japan, Aug. 14, 1967, 42/ 52,099 Int. Cl. 321d 13/20 U.S. Cl. 72-77 8 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to methods and apparatus for producing corrugations in metallic tubes and is characterized by the fact that it is possible to produce corrugations of various shapes by utilizing at least two corrugating rings or two sets of corrugating rolls. In particular the invention relates to methods and apparatus capable of producing easily corrugations of greater depth as compared with pitch, corrugations of a small pitch whose trough is wider than the crest (tubes with such corrugations have good bending characteristics and other mechanical properties and permit a cable to be pulled into them more easily), and furthermore corrugations conformable to the shapes of apexes of corrugating rings or rolls, without employing any core (corrugating tool to be applied inside the tube) as in the conventional apparatus.

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to methods and apparatus for producing corrugations in metallic tubes, and in particular proposes methods and apparatus capable of producing easily corrugation of greater depth as compared with pitch, corrugation of a small pitch whose trough is wider than the crest, and furthermore corrugation along shapes of apexes of corrugating rings or rolls without employing any core as in the conventional apparatus.

In the prior art there are two representative methods for corrugating a metallic tube.

The first is a method of corrugating by pressing a corrugating tool only against the exterior of a metallic tube, and the second is a method of corrugating by pressing a corrugating tool against the exterior of a metallic tube and simultaneously inserting also another corrugating tool (core) into the tube, thus nipping the tube wall between the two tools. However these methods have the following defects.

In the first method, in which corrugation is made by pressing a corrugating tool only against the exterior of the tube without producing any pressure from inside the tube, it is impossible to produce sharp corrugations having greater depth as compared with pitch or corrugations whose trough is wider than the crest. As shown in FIG. 1a, when a metallic tube 2 is corrugated by the first method, no sharp corrugations can be obtained even if the force F is applied to it by a corrugating tool 1 with relatively thin apex because the deformation range d of the tube is nearly determined by the size of a tube (thickness t, diameter D). Consequently if a tube of the same size as a tube having the corrugation as shown in FIG. 1a (pitch P, depth h) is corrugated at a pitch P as shown in FIG. 1b which is smaller than P in FIG. la, its outside diameter decreases, thereby producing only very shallow corrugations. The depth h becomes very small as compared with pitch P: in other words it is impossible to produce deep corrugations of a small pitch. Besides if the tube is corrugated at the same pitch P as shown in FIG. 1a by utilizing a corrugating tool 3 with an apex 3,568,489 Patented Mar. 9, 1971 of great width as in FIG. 10, the depth of corrugation It" becomes very small as described above because the deformation range d of a pipe is nearly constant according to a size of a pipe.

As above, by the first method, in which only the force in the radial direction is applied to the exterior of a metallic tube to be corrugated, it is impossible to produce sharp corrugations or corrugations whose trough is wider than the crest. Corrugations made by this method are very limited in form.

Then in order to produce sharp corrugations or corrugations whose trough is wider than the crest, the second method has been used, in which the corrugating force is applied not only to the exterior of a metallic tube, but also to its interior by utilizing a core.

However, because the length of the core is limited, it is difficult to produce long corrugated tubes. This method is unsuitable for producing many different sizes of tubes, because the core must be changed every time a tube of a different size is corrugated.

Furthermore, this method is impracticable for producing corrugations on cavity-filled tube, such as cable sheath having cable core, in which there is no room for the core to be inserted.

The present invention provides a new method for corrugating a metallic tube which is free from the defects of the above conventional corrugating methods. The first purpose of the present invention is to obtain sharply corrugated metallic tubes by applying force only against the exterior of tubes without employing a core. The second purpose of the present invention is to obtain corrugated metallic tubes in which despite a small pitch of corrugation, the trough is wider than the crest.

The third object of the present invention is to propose a method suitable for producing metallic tubes corrugated as above in a continuous length, that is to say, a method of corrugating tubes by at least two corrugating rings or two sets of rolls. The fourth object of the present invention is to propose a method for producing corrugation of shapes conformably to the shape of apexes of corrugating rings or rolls. The fifth object of the present invention is to propose a method of producing efficiently and at low cost corrugated tubes of various shapes, having good mechanical characteristics, which is convenient for the production of many different sizes of corrugated tubes.

The present invention provides methods and apparatus of producing a corrugated tube by pressing a corrugating tool against the exterior of a metallic tube, in which a plurality of corrugating tools are arranged in such a manner that their inner surfaces, which engage the tube, will come on the whole or part of the peripheries of the circles satisfying the conditions,

(1) The planes of the circles corresponding to adjacent corrugating tools are fiat, and said planes have different inclination angles respectively to the plane perpendicular to the central axis of a metallic tube to be corrugated, the inclination angle of the circle corresponding to a front one of said adjacent corrugating tools being preselected to be algebraically smaller than the inclination angle of the circle corresponding to a rear one of said corrugating tools, and

(2) The centers of the circles corresponding to the adjacent corrugating tools are displaced respectively from the center of the metallic tube in different radial directions relative to one another with the phase of the circle corresponding to the front one of said corrugating tools being in advance of the phase of the circle corresponding to the rear one of said corrugating tools.

Next, referring to the accompanied drawings the constitution of the invention will be explained in detail. FIG.

1 is a diagram for illustrating a conventional corrugating method. FIG. 2 is a diagram for illustrating the fundamental principle of the present invention. FIGS. 3a and b are vertical and transverse sectional views in which a portion is omitted and which show the first embodiment of the present invention respectively. FIGS. 4a and b are vertical and transverse sectional views in which a portion is omitted and which show the second embodiment of the present invention. FIGS. 5, 6 and 7 are diagrams for illustrating the theory of the present invention respectively. FIG. 8 is a vertical sectional view, in which a portion is omitted and which shows the third embodiment of the present invention. FIG. 9 is a diagram for explaining the principle of the fourth embodiment of the present invention. FIGS. 10a and b are diagrams of corrugation of a metallic tube corrugated by the method of the present invention and FIGS. 11a and b are diagrams of a metallic tube corrugated by methods of the present invention and the prior art respectively.

Firstly, to explain the principle of the present invention as shown in FIG. 2a, the force F is applied in the radial direction to the exterior of metallic tube 2 and simultaneously the force F in the axial direction of the tube, whereby forming corrugations in such a manner as if to pinch the wall 4 of a pipe. In this way it is possible to produce easily corrugations having both a small pitch p and great depth [1 without employing a core. Of course, as shown in FIG. 2b, because it is possible to apply the force F along the axial direction of a pipe even though the width w of the apex of a corrugating tool 3 is large, it is possible to produce easily corrugations having a large depth h whose trough is wider than the crest.

In this way the present invention is based on my findings that a metallic pipe is easily deformed when the force is applied to the axial direction as well as in the radial direction. This may be due to the fact that any metal material, which is in its plastic region owing to a force given it in one direction. is easily deformed when additionally given even a slight force in a different direction.

Next, embodiments of the present invention will be ex plained. In FIGS. 3a and b, is a metallic tube to be corrugated, 6 the inside surface of the root of a corrugated metallic tube, and 7 a bush. The metallic tube 5 is sent out in the direction of the arrow in FIG. 3a. 8, 9 are corrugating tools of ring shape. Their inside surfaces contacting with the tube are situated on the peripheries of circles 11 and 12. Circles 11 and 12 are as follows.

(1) These circles are planar and have different slant angles and to the plane perpendicular to the central axis of a metallic tube to be corrugated, and the slant angle of the circle of the rear corrugating tool 9 is intensionally made smaller algebraically than the slant angle ra of the circle of the rear corrugating tool 8.

(2) The centers of the circles are displaced from the center of the tube by H and H in different directions and also the phase of the circle of the front corrugating tool 9 is in advance of the phase of the circle of the rear corrugating tool 8.

The adjacent corrugating tools 8 and 9 as described above are caused to rotate about the central axis 10 of a metallic tube 5 at the same speed and in the same direction by driving gear (not shown), and thereby a metallic tube 5 is pressed by the tool on its exterior and corrugated spirally. In this way the force in the axial direction is further applied by the front tool 9 to the corrugations formed by the rear tool 8, thereby easily producing sharp corrugations or corrugations whose trough is wider than the crest.

FIG. 4 shows corrugating tools 13 and 14 comprising a plurality of rolls and in this case the apexes of the rolls contacting with 4 a metallic tube are situated on the peripheries of circles 15 and 16 similar to 11 and 12 of FIG. 3b.

Hereinbefore the concept of the present invention has been explained. Now the present invention is explained theoretically by utilizing formulas.

Firstly an inner surface of a corrugating ring is arranged on the periphery of a circle of a radius R,, and inclined at an angle of relative to a plane perpendicular to a central axis 18 of a metallic tube 17 of a radius R to be corrugated as shown in FIG. 5. The center O is eccentric from H to a point, O on a central axis 18 of a metallic tube, and the said corrugating tool is rotated about a central axis 18, while the inclination and eccentric distance H are maintained to produce spiral corrugations on a metallic tube 17. Now looking at an optional point Q on a metallic tube 17 in FIG. 5, we see that Q is pressed in gradually by the corrugating tool to the depth of h and that then the corrugating tool comes off gradually. The displacement of the apex of the corrugating tool in the radial direction of the tube h and the displacement of the apex of the tool in the axial direction of the tube 2 are the functions of the rotating angle of the tool. Then the relation between the radial displacement, h. the axial displacement Z and the rotating angle 0 is obtained in an equation as follows:

(1) In a triangle O O P Then in the actual design, the eccentricity H (=0 0 is usually very small as compared with a radius of a metallic tube R (=O P), so 4 O PO 1 Therefore UF=.@+Q

(3) Then Z=R sin From the Formulas 6 and 7 Z=R tan 9 sin (l9d /1 tan 51 sin (0-0 As above, the relation between the rotating angle on one hand and the radial displacement h and the axial displacement Z on the other at a certain point on the circumference of a metallic tube is shown in Formulas and 8. As, however, the inclination 4 is small and 51 is equal to or less than 95,,

cosf'; land tanff Therefore, the final equations are as follows.

Z=R osin (00 )hosin (0-0,)

By substituting actual figures in Formulas 9 and 10, it is possible to obtain a locus of the apex of a corrugating tool on the side of the tube. For example in FIG. 6 a locus 20 is traced by a point 22 of the apex of a rear corrugating tool 21 making one revolution when R =R =47.5 mm.

h =5 mm., and 55 :5". Besides a locus 23 of FIG. 6 is traced by an apex 25 of a front tool 24 making one revolution when R =45.5 mm., R =47.-5 mm., h =5 mm. and =1. Now, corrugation on the metallic tube 17 by tools 21 and 24 having the above loci will be explained with reference to FIG. 6.

The axial displacement shown by the locus 20 of the apex 22 of the rear corrugating tool 21 is larger than that shown by the locus 23 of the apex of a front corrugating tool 24. Therefore if, as a metallic tube 17 is travelled in the direction of arrow at a constant speed, adjacent corrugating tools 21 and 24 are rotated about the central axis of the tube in the same direction and at the same speed while the above inclination and eccentric distance are maintained, the speed at which the tube passes rear tool 21 is higher than that at which it passes the front tool 24 by which the force is applied to corrugations formed by rear tool 21 in the direction of tube axis to reduce the pitch of corrugations to an extent corresponding to the difference between the two speeds. The curves in FIG. 6 show the process of corrugating a metallic tube, by Way of a line on the circumference of the tube and in parallel to its axis (at top part of the tube in the figure). When the tool 21 is situated at a position (D, a certain position on the outside surface of a metallic tube contacting with the tool 21 is represented by a mark I, and similarly when a tool 21 moved to positions (2),

, the corresponding positions on the outside surface of a metallic tube are represented by marks II, III, IV Further when a tool 24 is situated at a position a certain point on the surface of a metallic tube lying nearly under the tool 24 is represented by I, and when the tool 24 moved to positions Supposing that at this time, a tool 24 is for example at a position position but a point I on a metallic tube lying in the vicinity of the tool 24 moves merely to II because its displacement in the axial direction of the tube is small. This is to say, the tool 24 performs braking action which prevents the progress of a metallic tube and in other words the force reverse to the direction of progress of a metallic tube is applied. This forms corrugations as shown by to the position f\ J Besides if a corrugating tool rotates by thirty degrees, a tool 21 presses a metallic tube and moves to position and the point II on a metallic tube moves to III, but a point II on the tube moves slightly to III because the tool 24 moves merely from the position and thereby the action of braking the progress of the tube generates as above and the force is applied to tube in its axial direction as described above, so that corrugation becomes sharp as In the same manner the corrugation is made sharper and sharper by the force caused by the tools 21 and 24 which works as if to pinch the crest. When the tool 24 comes at a position it no longer contacts with the crest of corrugation so that no braking action works on the tube in its axial direction and the crest of corrugation freely passes the position of the tool 24. When by further rotation the tool 21 returns to the original position and the tool 24 to the position the process as described above is repeated again.

The important points in the above explanation are that there is a difference in phase between the tools 21 and 24 adjacent each other so that the front tool 24 is at the position when the rear tool 21 is at the position (D, and that the phase of the circle of which the portion contacted to the metallic tube 17 of the front tool 24 is present at the periphery thereof is in advance of the phase of the circle of the rear tool 21. As clear from Formulas 9 and 10, this can be attained by providing a deviation between the initial phase of the tool 21 and that of the tool 24 and advancing by the deviation the initial phase 0,, of the front tool 24 over that of the rear tool 21 to the direction of the rotation. FIG. 6 shows the case where the phase difference is 60 and the phase of the circle of the front tool 24 is in advance of the phase of the circle of the rear tool 21 by the phase difference. In FIGS. 7a, b, and c, the

phase difference is the angle formed by a line between 0,, and

and a line between 0 and @cn av representing the points closest to O the center of the tube and on the circles 26 and 27 respectively on which are located such portions of the tools 21 and 24 as are in contact with the tube. In the above explanation of the present invention, it was described that the centers of circles, on which are located the parts of corrugating tools contacting with the tube, are respectively eccentric in the different directions to the central axis of the tube. Such eccentric arrangement of the tools makes the phase difference The above explanation involves a case in which the values of inclinations and 0 of the two corrugating tools were of the same sign, but they need not necessarily be so. In Formulas 9 and l0, 4),, and may be given values of different signs. For example, in FIG. 6, when the inclination =1) of the tool 24 is changed to =-l) the locus of the apex of the tool 24 is formed in a direction opposite to the arrow, namely, in the clockwise direction in the figure. Yet, it will be understood that the effect of pinching up corrugation can be obtained similarly. Namely, as shown in FIG. 8 even though the direction of inclination of the rear corrugating ring 21 and that of the front corrugating ring 24 are made different from each other, it is possible to embody the present invention The above embodiments explain that the depth of corrugation is determined only by the rear ring, but there is a certain limitation to the depth of corrugation formed by a single ring and the ring is forcibly pressed onto the tube beyond such limit, to exert the undesirable influence on mechanical characteristic such as that it often causes buckling of the tube. Therefore, when very deep corrugations are required, it is desirable to corrugate the tube in two steps, forming shallow corrugations with a rear corrugating ring and making them deeper to the desired depth with a front corrugating ring.

Of course, also in this case the force in the axial direction of a tube is caused by the front corrugating ring. As compared with the case in which the front ring makes no further depression, this method has particularly great effects as follows.

As shown in FIG. 9, when after corrugations are made to a depth of h by a force F given by the rear corrugating ring, a force F is applied in the direction perpendicular to the tube axis to make corrugations deeper by h while a force F simultaneously works in the axial direction of the tube, the shape of the corrugations can be easily made more comformably to the contour of the apex of the corrugating ring than when the front ring gives only a force in the axial direction of the tube.

This may be because in the two-step depression, the area of a tube where it turns into the plastic region by the depressive force given by the front ring becomes larger than in the case of FIG. 2a where only a force is the axial direction of the tube is given by the front ring. FIG. a shows a case were the depressive force is applied only by the rear ring and only the force in the axial direction of a tube is applied by the front ring. Sharp corrugations are produced by the pinching-up effect, but the contour of one side of a corrugation is different from that of the other side (not symmetrical), so that the corrugation does not conform to the shape of the apex of a corrugating ring. However, when the front ring gives a force in the axial direction of the tube while making further depression to form deeper corrugations, the pinching-up effect works more effectively and as shown in FIG. 10b produces symmetrical corrugations conformable to the shape of the apex of the ring.

In the above description, the principle and embodiments in the case in which the two corrugating tools are employed were explained in detail, and it goes without saying that it is possible to corrugate a metallic tube according to the similar principles even though three or four corrugating tools are employed. The present invention can be embodied generally by employing a plurality of corrugating tools. Besides it goes without saying that a corrugated tube referred to in the present invention includes a corrugated sheath of an electric cable in addition to a non-filled corrugated tube.

The material of the corrugating tools used in the present invention is not limited to metals. Plastics or any other material may be used for them. Moreover the tools may take any other shape than ring or roll.

FIG. 11 shows a corrugation a produced in a metallic tube according to the present invention and FIG. 11 also shows a corrugation b produced according to the conventional method in which the force is applied only in the radial direction of a metallic tube. As apparent from the comparison of those corrugations, corrugations made by only one corrugating tool as in the conventional method are shallow and gently sloping and the resultant corrugated tube has unsatisfactory bending characteristic. According to the present invention it is possible to produce deeply and sharply corrugated tubes having good bending characteristics.

What I claim is:

1. A method of producing a corrugated metallic tube comprising the step of pressing from the external side of a metallic tube by means of a plurality of adjacent corrugating tools, said pressing step including disposing the portions of said corrugating tools to be brought into contact with the metallic tube at the peripheries of circles satisfying the following conditions:

(1) the planes of the circles corresponding to the adjacent corrugating tools are flat, and said planes have different inclination angles respectively to the plane perpendicular to the central axis of a metallic tube to be corrugated, the inclination angle of the circle corresponding to a front one of said adjacent corrugating tools being preselected to be algebraically smaller than the inclination angle of the circle corresponding to a rear one of said corrugating tools, and

(2) the centers of the circles corresponding to the adjacent corrugating tools are displaced respectively from the center of the metallic tube in different radial directions, the phase of the circle corresponding to the front one of said corrugating tools being in advance of the phase of the circle corresponding to the rear one of said corrugating tools,

and rotating the corrugating tools about the central axis of said metallic tube at the same speed and in the same direction, whereby a pressing force is applied from exterior of the tube in a radial direction relative to the metallic tube and, at the same time, a pressing force is also applied in an axial direction relative to the metallic tube to pinch up the wall of the metallic tube and to form a helical corrugation in the metallic tube.

2. An apparatus for producing a corrugated metallic tube comprising a pair of adjacent corrugating tools, the portions of said corrugating tools to be brought into contact with a metallic tube for pressing the exterior of the metallic tube being disposed respectively at the peripheries of circles satisfying the following conditions:

(1) the planes of the circles corresponding to the adjacent corrugating tools are tlat, and said planes have dilferent inclination angles respectively to the plane perpendicular to the central axis of a metallic tube to be corrugated, with the inclination angle of the circle corresponding to the front one of the corrugating tools being preselected to be algebraically smaller than the inclination angle of the circle corresponding to the rear one of said corrugating tools, and

(2) the centers of the circles corresponding to the adjacent corrugating tools are displaced respectively from the center of the metallic tube in different radial directions, the phase of the circle corresponding to the front corrugating tool being in advance of the phase of the circle corresponding to the rear corrugating tool,

and a driving means for rotating the corrugating tools about the central axis of the metallic tube at the same speed and in the same direction.

3. A method of producing a corrugated metallic tube as in claim 1 wherein two corrugating tools are used, the rear corrugating tool depressing a metallic tube in the direction perpendicular to the axis of said tube to form corrugations and the front corrugating tool depressing the troughs of said corrugations further in the direction perpendicular to the tube while simultaneously giving a force to the tube in the axial direction thereof.

4. The method of claim 1 for producing a corrugated metallic tube wherein metallic tube rings are used as corrugating tools.

5. The apparatus of claim 2 for producing a corrugated metallic tube which uses rings as corrugating tools.

6. The method of claim 1 for producing a corrugated metallic tube wherein said corrugating tools are composed of a plurality of rolls.

7. The apparatus of claim 2 for producing a corrugated metallic tube which uses corrugating tools composed of a plurality of rolls.

8. The method of claim 1 wherein the metallic tube is the sheath of an electric cable.

References Cited UNITED STATES PATENTS 1,919,254 7/1933 Picece et al. 7277 2,419,678 4/1947 Duenas et al. 7277 3,128,821 4/1964 Anderson 7277 3,353,389 11/1967 Kelstrom 7277 FOREIGN PATENTS 222,133 9/ 1958 Australia.

RICHARD J. HERBST, Primary Examiner 

